In oil and gas well completion operations, frac or bridge plugs are necessary for zonal isolation and multi-zone hydraulic fracturing processes. The advantages of frac and bridge plugs made primarily from composite materials is well established since these products significantly reduce drill-out (removal) time compared to all metallic frac and bridge plugs. However, as drilling for oil and gas extends deeper and/or fracking pressures increase, composite frac and bridge plugs are now expected to meet higher operating pressures and temperatures. Higher temperatures and pressures put severe stresses on the composite frac or bridge plug components that are thought to already operate at or near their operating limits. It is therefore necessary to optimize the design of the composite frac or bridge plug components to meet still yet higher operational requirements with necessary strength. It is also necessary to optimize downhole tools for lower cost since they are an expendable item in well completion.
A typical frac or bridge plug is configured to be positioned in and seals a well casing pipe by actuating serrated wedge slips that dig into the inner wall of the casing as the frac or bridge plug is set. There are typically 4-8 serrated wedge slip elements that are forced out against the well pipe casing by tapered cones located on the frac or bridge plug mandrel that have flat notches machined into the outer surface. The notches in the cone act as a guide for the slips and provide the inclined wedge necessary to force the slips into the well pipe inner wall when the frac or bridge plug is set.
As a result of these complex outer surface features, both the upper and lower cones of a frac or bridge plug are difficult to make and therefore expensive. The lower cone in a typical frac or bridge plug is more highly loaded in operation than the upper cone. For this reason, more expensive materials and processes are required to make the cones but especially the lower one.
While upper cones can be compression molded or injection molded from advanced fiber-filled polymers, the lower cone is typically made from wrapped high strength fiberglass cloth pre-impregnated with epoxy resin in order to be strong enough to resist the compressive forces of the inclined wedges that keep the frac or bridge plug from being pushed down the well during fracking. A typical high strength lower cone is made out of a billet of fiberglass material that is first formed by wrapping pre-preg fiberglass cloth material and curing it with heat. The billet is then machined into the final lower cone shape that includes faceted surfaces for the wedge slips to interface with. The machining of the fiberglass billet is particularly expensive and difficult due to the abrasive nature of the composite cone material.